/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.orm.jpa.support;

import org.springframework.dao.DataAccessResourceFailureException;
import org.springframework.lang.Nullable;
import org.springframework.orm.jpa.EntityManagerFactoryUtils;
import org.springframework.orm.jpa.EntityManagerHolder;
import org.springframework.transaction.support.TransactionSynchronizationManager;
import org.springframework.util.StringUtils;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.request.async.CallableProcessingInterceptor;
import org.springframework.web.context.request.async.WebAsyncManager;
import org.springframework.web.context.request.async.WebAsyncUtils;
import org.springframework.web.context.support.WebApplicationContextUtils;
import org.springframework.web.filter.OncePerRequestFilter;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.PersistenceException;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * Servlet Filter that binds a JPA EntityManager to the thread for the
 * entire processing of the request. Intended for the "Open EntityManager in
 * View" pattern, i.e. to allow for lazy loading in web views despite the
 * original transactions already being completed.
 *
 * <p>This filter makes JPA EntityManagers available via the current thread,
 * which will be autodetected by transaction managers. It is suitable for service
 * layer transactions via {@link org.springframework.orm.jpa.JpaTransactionManager}
 * or {@link org.springframework.transaction.jta.JtaTransactionManager} as well
 * as for non-transactional read-only execution.
 *
 * <p>Looks up the EntityManagerFactory in Spring's root web application context.
 * Supports an "entityManagerFactoryBeanName" filter init-param in {@code web.xml};
 * the default bean name is "entityManagerFactory". As an alternative, the
 * "persistenceUnitName" init-param allows for retrieval by logical unit name
 * (as specified in {@code persistence.xml}).
 *
 * @author Juergen Hoeller
 * @see OpenEntityManagerInViewInterceptor
 * @see org.springframework.orm.jpa.JpaTransactionManager
 * @see org.springframework.orm.jpa.SharedEntityManagerCreator
 * @see org.springframework.transaction.support.TransactionSynchronizationManager
 * @since 2.0
 */
public class OpenEntityManagerInViewFilter extends OncePerRequestFilter {

    /**
     * Default EntityManagerFactory bean name: "entityManagerFactory".
     * Only applies when no "persistenceUnitName" param has been specified.
     *
     * @see #setEntityManagerFactoryBeanName
     * @see #setPersistenceUnitName
     */
    public static final String DEFAULT_ENTITY_MANAGER_FACTORY_BEAN_NAME = "entityManagerFactory";


    @Nullable
    private String entityManagerFactoryBeanName;

    @Nullable
    private String persistenceUnitName;

    @Nullable
    private volatile EntityManagerFactory entityManagerFactory;

    /**
     * Return the bean name of the EntityManagerFactory to fetch from Spring's
     * root application context.
     */
    @Nullable
    protected String getEntityManagerFactoryBeanName() {
        return this.entityManagerFactoryBeanName;
    }

    /**
     * Set the bean name of the EntityManagerFactory to fetch from Spring's
     * root application context.
     * <p>Default is "entityManagerFactory". Note that this default only applies
     * when no "persistenceUnitName" param has been specified.
     *
     * @see #setPersistenceUnitName
     * @see #DEFAULT_ENTITY_MANAGER_FACTORY_BEAN_NAME
     */
    public void setEntityManagerFactoryBeanName(@Nullable String entityManagerFactoryBeanName) {
        this.entityManagerFactoryBeanName = entityManagerFactoryBeanName;
    }

    /**
     * Return the name of the persistence unit to access the EntityManagerFactory for, if any.
     */
    @Nullable
    protected String getPersistenceUnitName() {
        return this.persistenceUnitName;
    }

    /**
     * Set the name of the persistence unit to access the EntityManagerFactory for.
     * <p>This is an alternative to specifying the EntityManagerFactory by bean name,
     * resolving it by its persistence unit name instead. If no bean name and no persistence
     * unit name have been specified, we'll check whether a bean exists for the default
     * bean name "entityManagerFactory"; if not, a default EntityManagerFactory will
     * be retrieved through finding a single unique bean of type EntityManagerFactory.
     *
     * @see #setEntityManagerFactoryBeanName
     * @see #DEFAULT_ENTITY_MANAGER_FACTORY_BEAN_NAME
     */
    public void setPersistenceUnitName(@Nullable String persistenceUnitName) {
        this.persistenceUnitName = persistenceUnitName;
    }

    /**
     * Returns "false" so that the filter may re-bind the opened {@code EntityManager}
     * to each asynchronously dispatched thread and postpone closing it until the very
     * last asynchronous dispatch.
     */
    @Override
    protected boolean shouldNotFilterAsyncDispatch() {
        return false;
    }

    /**
     * Returns "false" so that the filter may provide an {@code EntityManager}
     * to each error dispatches.
     */
    @Override
    protected boolean shouldNotFilterErrorDispatch() {
        return false;
    }

    @Override
    protected void doFilterInternal(
            HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
            throws ServletException, IOException {

        EntityManagerFactory emf = lookupEntityManagerFactory(request);
        boolean participate = false;

        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
        String key = getAlreadyFilteredAttributeName();

        if (TransactionSynchronizationManager.hasResource(emf)) {
            // Do not modify the EntityManager: just set the participate flag.
            participate = true;
        } else {
            boolean isFirstRequest = !isAsyncDispatch(request);
            if (isFirstRequest || !applyEntityManagerBindingInterceptor(asyncManager, key)) {
                logger.debug("Opening JPA EntityManager in OpenEntityManagerInViewFilter");
                try {
                    EntityManager em = createEntityManager(emf);
                    EntityManagerHolder emHolder = new EntityManagerHolder(em);
                    TransactionSynchronizationManager.bindResource(emf, emHolder);

                    AsyncRequestInterceptor interceptor = new AsyncRequestInterceptor(emf, emHolder);
                    asyncManager.registerCallableInterceptor(key, interceptor);
                    asyncManager.registerDeferredResultInterceptor(key, interceptor);
                } catch (PersistenceException ex) {
                    throw new DataAccessResourceFailureException("Could not create JPA EntityManager", ex);
                }
            }
        }

        try {
            filterChain.doFilter(request, response);
        } finally {
            if (!participate) {
                EntityManagerHolder emHolder = (EntityManagerHolder)
                        TransactionSynchronizationManager.unbindResource(emf);
                if (!isAsyncStarted(request)) {
                    logger.debug("Closing JPA EntityManager in OpenEntityManagerInViewFilter");
                    EntityManagerFactoryUtils.closeEntityManager(emHolder.getEntityManager());
                }
            }
        }
    }

    /**
     * Look up the EntityManagerFactory that this filter should use,
     * taking the current HTTP request as argument.
     * <p>The default implementation delegates to the {@code lookupEntityManagerFactory}
     * without arguments, caching the EntityManagerFactory reference once obtained.
     *
     * @return the EntityManagerFactory to use
     * @see #lookupEntityManagerFactory()
     */
    protected EntityManagerFactory lookupEntityManagerFactory(HttpServletRequest request) {
        EntityManagerFactory emf = this.entityManagerFactory;
        if (emf == null) {
            emf = lookupEntityManagerFactory();
            this.entityManagerFactory = emf;
        }
        return emf;
    }

    /**
     * Look up the EntityManagerFactory that this filter should use.
     * <p>The default implementation looks for a bean with the specified name
     * in Spring's root application context.
     *
     * @return the EntityManagerFactory to use
     * @see #getEntityManagerFactoryBeanName
     */
    protected EntityManagerFactory lookupEntityManagerFactory() {
        WebApplicationContext wac = WebApplicationContextUtils.getRequiredWebApplicationContext(getServletContext());
        String emfBeanName = getEntityManagerFactoryBeanName();
        String puName = getPersistenceUnitName();
        if (StringUtils.hasLength(emfBeanName)) {
            return wac.getBean(emfBeanName, EntityManagerFactory.class);
        } else if (!StringUtils.hasLength(puName) && wac.containsBean(DEFAULT_ENTITY_MANAGER_FACTORY_BEAN_NAME)) {
            return wac.getBean(DEFAULT_ENTITY_MANAGER_FACTORY_BEAN_NAME, EntityManagerFactory.class);
        } else {
            // Includes fallback search for single EntityManagerFactory bean by type.
            return EntityManagerFactoryUtils.findEntityManagerFactory(wac, puName);
        }
    }

    /**
     * Create a JPA EntityManager to be bound to a request.
     * <p>Can be overridden in subclasses.
     *
     * @param emf the EntityManagerFactory to use
     * @see javax.persistence.EntityManagerFactory#createEntityManager()
     */
    protected EntityManager createEntityManager(EntityManagerFactory emf) {
        return emf.createEntityManager();
    }

    private boolean applyEntityManagerBindingInterceptor(WebAsyncManager asyncManager, String key) {
        CallableProcessingInterceptor cpi = asyncManager.getCallableInterceptor(key);
        if (cpi == null) {
            return false;
        }
        ((AsyncRequestInterceptor) cpi).bindEntityManager();
        return true;
    }

}
